The present invention is directed to adhesive tapes and, more particularly, to duct tapes having a backing which is more cost-effective to manufacture. In its simplest form, duct tapes comprise a cloth material carrying an adhesive layer on one surface thereof Commercially available duct tapes additionally have an outer water-impermeable, flexible plastic laminated to the cloth layer. The cloth layer provides reinforcement and increased tensile strength and the backing is typically about 1-4 mils thick and provides the requisite dimensional stability to the tape. Conventionally, the backing material has been formed from a flexible plastic support, e.g. a cellulose ester such as cellulose acetate, cellulose triacetate, and the like; a polyester such as polyethylene terephthalate; or a polyolefin such as polyethylene or polypropylene. Most typically, the backing has been formed from polyethylenes, e.g. low density, high density, or linear low density polyethylene, including mixtures thereof.
While duct tapes have achieved wide market acceptance, there is a need for a duct tape that can be manufactured more cost effectively whereby the cost for producing a tape of comparable end use properties may be significantly reduced.
In accordance with the present invention, attention has been focused on developing a more cost efficient substitute for polyolefin backings. Conventionally polyolefin backings used in the manufacture of duct tape have been formed using a blown film extrusion process and coated on one side with a release agent which enables the tape to be wound into a roll and readily unwound. In the blown film process a film is blown from the extruder die and this film is compressed as it is passed between a pair of nip rollers. The blown film extrusion process is comparatively expensive to perform and the additional manufacturing step of coating the backing with a release agent further adds to the cost of manufacturing the product.
In accordance with the present invention, a support for duct tape is provided which is a co-extruded laminate comprising a D layer of low density polyethylene (LDPE), a first B layer of a blend of LDPE and high density polyethylene (HDPE), a C layer of a blend of LDPE and a pigment, a second B layer, and an A layer of LDPE which preferably includes a release agent. LDPE and HDPE polymers are commodity materials available from Exxon Corporation and Dow Chemical Company. The backing is typically about 1 to 4 mils thick. When the A layer contains a release agent, it provides a release surface that enables the tape to be self-wound to form a roll and dispensed by unwinding without undue force. The layers typically constitute the following approximate proportions by weight of the backing:
This backing has many of the advantages of backings formed by the blown film extrusion method but can be manufactured using a less expensive cast coextrusion process. Furthermore, in accordance with the preferred embodiment of the invention, a release agent is incorporated into the lamina on the surface opposite the adhesive (i.e., the A layer) thereby obviating the application of the release agent as a separate process.
Adhesive tapes in accordance with the invention comprise a laminar structure comprising, in order, a coextruded backing as herein described in detail, a cloth scrim; and a layer of adhesive, e.g. pressure-sensitive adhesive.